A parallel station heuristic for the mixed-model production line balancing problem

Demand for customized products and proliferation of optimal features have increased the need for flexible assembly systems that are capable of simultaneously producing multiple versions of similar products. Serial assembly systems have traditionally been used for the production of a single product type, and more recently for mixed model production. In this paper, a nonlinear integer program is proposed as a model for the production line balancing problem. This problem entails the assignment of tasks to stages in a serial production line. The model allows mixed-model production and the use of identical parallel workstations at each stage of the serial production system. The objective function trades off idle workstation time with duplication of task-dependent equipment/tooling cost. A heuristic is developed to create parallel workstations and assign tasks. Station utilization is also explicitly considered by using a threshold variable for target (acceptable) levels. The procedure is illustrated with an example. Computational experiments are also provided to analyse the performance of the heuristic.